LocoBuffer-II General Information

(Updated 3 May, '05)

The LocoBuffer II is currently the most reliable way to connect a computer to a LocoNet®. This Ready To Run commercial unit is produced by RR-CirKits, and based in part on the original LocoBuffer design.

Note: For those that want to build up their own LocoBuffer you may get parts and boards from Hans deLoof.

LocoBuffer-II Rev-f schematic.

Schematic notes: This new schematic is for the revised version of the LocoBuffer-II. These revisions include extensive internal changes to convert it to SMT technology, but no functional changes of importance to the user. We originally considered calling this a LocoBuffer-III due to the large number of changes, but decided that functionally it was still a LocoBuffer-II, and that shall remain it's name.


LocoBuffer-II Features:

LocoBuffer-II System Recommendations:

Laptop with Serial Port - LocoBuffer-II

Desktop with Serial Port - LocoBuffer-II-P

Laptop or Desktop with USB only - LocoBuffer-II-P-USB

Mac with DIN-8 - LocoBuffer-II-P-Mac

Mac with USB only - LocoBuffer-II-P-USB

Recommended setup

The recommended basic setup for the LocoBuffer II is:

Basic LocoBuffer-II sanity test

To perform a very basic LocoBuffer-II sanity test do the following.


  1. Unplug the LocoNet® cable. Remove the internal LocoNet® terminator if it is installed.
  2. Set Sw 7-8 ON, if they are not already.
  3. Power up the LocoBuffer-II from a wall wart. Both green power LED's should come on, then the red activity LED should come on after a very short delay.
  4. Plug in the LocoNet® cable. The red activity LED should go out.
  5. Restore SW 7-8 to their original position if necessary.

Explanation of the above is as follows. Unplugging the LocoNet® cable removes the termination. Power up with Sw 7-8 closed powers both sides of the unit which lights both green LED's. The processor boots up and after a short (barely noticeable) delay starts monitoring the status of the LocoNet®. With no termination the LocoNet® looks like it is "busy" so the processor lights the red activity light. When the LocoNet® cable is plugged in it sees the command station and it no longer appears that the LocoNet® is "busy", so the activity LED is extinguished. This simple test shows that the LocoBuffer-II power circuits are OK, that it can read the LocoNet® status, and that the processor is running. It does not test any of the serial port connections, nor the capability to send commands to the LocoNet®. Note: If there is a noticeable delay of about 1 second before the LED lights, then the LocoBuffer-II boot loader code may be missing. This will not be a problem unless you need to upgrade the firmware. (currently there are no upgrades to the firmware)

If the activity LED does not extinguish when you plug in the LocoNet® cable, be sure that your DCC command station is powered up, then check your LocoNet® wiring. To further test the LocoBuffer-II do the following Loop Back Test.

Loop Back Test (Wrap-around testing)

The LocoBuffer-II input circuit and code actually reads from the LocoNet® output jack, so if you install the LocoNet® terminator (the small circuit that is shipped with the LocoBuffer II) and set SW7-8 to ON (down) so that the LocoNet® circuitry gets it's power from the wall wart, then you have created a loop back test. The only thing that is not tested is the LocoNet® jack itself.


  1. Unplug the LocoNet® cable
  2. Open case (use a small screw driver to work open the latches at the small slots on the sides)
  3. Install terminator board
  4. Set Sw 7-8 ON, all other switches OFF
  5. Set the JMRI LocoBuffer options to 19,200 baud and hardware handshaking enabled
  6. Open the JMRI LocoNet® Monitor window.
  7. Using JMRI send some commands (e.g. switch commands)
  8. The commands should appear in the LocoNet® monitor window and the LocoBuffer-II activity LED should blink
  9. Remove the terminator (unless your application requires it)
  10. Restore the LocoBuffer-II option switches to their normal settings for your application

LocoBuffer-II hex code download (1.632)

LocoBuffer-II boot loader code download

LocoBuffer-II Parts list

LocoBuffer-II Schematic

LocoBuffer-II Parts Layout

Image of production unit without it's case

Macintosh serial cable wiring

MS-Windows XP wiring concerns.

MS-Windows XP users must be sure that the cable and adapters they use include wiring for the DTR and DSR lines as well as the RTS and CTS lines. Failure to check this can cause failure of the connection on MS-Windows XP machines. If you are using an older DB-25 cable or connection plus an adapter to 9 pins, be especially sure that the adapter includes all the lines. Some that were originally included with serial mice do not.